UK defence and security firm Qinetiq has seen half-year profits rise 9%, boosted by sales in the US.

Pre-tax profit was £25.9m ($12.6m) in the six months to 30 September, up from £23.7m in the same period a year ego.

Qinetiq listed on the London Stock Exchange in February 2006, after the Ministry of Defence sold off a stake in the firm to a private equity company.

The sale has proved controversial, with the government accused of selling the stake too cheaply.

A third of Qinetiq was sold to the US private equity group, Carlyle, for £42m in 2003. By the time it listed on the stock exchange last year, the value of the stake had jumped to in value to £372m.

The government has also been criticised for agreeing to a sale that allowed Qinetiq's top staff to make millions of pounds in profits.

A report by the National Audit Office (NAO) on Friday said that UK taxpayers could have gained "more money" from the privatisation of Qinetiq.

The government defended the move and said it was excellent value for money.

Following its latest results, Qinetiq's chief executive Graham Love said: "The North American defence and security market continues to provide the greatest opportunity for expansion within the group and in the period this sector has driven strong order and turnover growth."

Revenues in North America hit £256.6m - marking an increased of 54.8% over six months.